Dynaco (a division of Radial Engineering Ltd.) is excited to re-launch the legendary tube amp, the ST-70 Series 3, this summer. The ST-70 Series 3 builds upon the proven design philosophies of the original David Hafler-designed Stereo 70, with contemporary design techniques resulting in exceptional performance improvements that meet the requirements of modern audiophiles.
The new Dynaco ST-70 Series 3 tube amplifier is rated at 35 watts per channel and switchable between both 4 and 8 Ohm outputs and features a Class-A push-pull stereo topography.
Dynaco engineers have made extensive use of high-quality parts that were unavailable at the time of the original design including precision metal-film resistors, poly-composition capacitors and miniaturized high-capacity power supply electrolytic capacitors. In addition, many of the newer parts are also built to tighter specifications than the originals. For instance, the PCB is constructed of military-grade, double-sided epoxy fiberglass PC material. In compliance with modern practices, the speaker binding posts have been updated, and a heavy-duty three-pin detachable grounded power cord is provided. Signal ground is the same as electrical ground and chassis, and all signal connectors are gold-plated.
The latest rendition has seen a substantially overhauled power supply from the original version, employing a larger dual-primary power transformer with improved line regulation, increased filter capacitance, and a solid-state rectifier that results in a much more articulate response. The resulting bottom end is a dramatic improvement over the original Stereo 70’s low-end response. This is augmented with a three-position high-pass filter switch to allow listeners to tailor the low-end response of the amplifier to their personal tastes.
The redesigned front end of the Series 3 amplifier replaces the obsolete 7199 pentode signal tubes from the original Stereo 70 with more commonly-used 12AU7 dual-triode tubes as part of a configuration that harkens back to the classic Williamson amplifier – this in itself has a long-storied history in the audiophile community. The output stage and EL34/6CA7 output tubes retain the same elements as the original Stereo 70 yet with the new design, the bias adjustment for the output tubes can be individually set using a front-panel recessed trimmer for each tube. After a warm up period (and with no input signal present), the bias is easily set by matching the brightness of the front-panel LEDs. Tremendous effort was applied to improving upon the original output transformers in an effort to increase damping and tighten up the low frequency response . A rear-panel switch allows the listener to select between 4 and 8-Ohm speaker loads. The feedback location is also configured by this switch, and the gain is adjusted accordingly. This results in an improved transient response when compared to older Stereo 70 implementations.
Building on the legacy of David Hafler’s enormously successful Stereo 70, the new Dynaco ST-70 Series 3 incorporates advancements in component quality, improvements to the electronic circuit performance and an all new design that is sure to please the most demanding audiophile.
For more info, jump to www.hafler.com